Future Value Interest Factor (FVIF)

fvif.php

<?php

/**
 * Future Value Interest Factor (FVIF)
 *
 * @param float $interest annual interest
 * @param int $periods periods
 * @throws InvalidArgumentException if $interest is not float
 * @throws InvalidArgumentException if $periods is not int
 * @return float future value interest factor
 */
function fvif($interest, $periods)
{
	if(!is_float($interest))
	{
		throw new InvalidArgumentException('$interest is not float');
	}

	if(!is_int($periods))
	{
		throw new InvalidArgumentException('$periods is not int');
	}

	if($periods == 0)
	{
		return 1;
	}

	$interest_factor = $interest + 1;

	if($interest_factor == 0)
	{
		return 0;
	}

	if($periods == 1)
	{
		return $interest_factor;
	}

	if($periods < 0)
	{
		$periods = -$periods;

		$interest_factor = 1 / $interest_factor;
	}

	return pow($interest_factor, $periods);
}

?>